Diagrams and Modelling Tools (Years 11 and 12)

Data flow diagram (DFD) Diagram

A diagram that shows how data moves through a system between processes, data stores and external entities.

Example: 'Voting system: voter, vote data, count.'

DFD process (circle) Diagram

A circle is a process: it uses input(s) to generate output(s). Name it with a verb phrase.

Example: 'Process: Validate login.'

Check this one: Not found word-for-word in the supplied syllabus, specifications, marking guidelines or notes; the definition is standard computing knowledge, so check it against your class notes.

DFD data store Diagram

A data store is an electronic file or non-computer storage (a filing cabinet), shown as an open rectangle or two parallel lines.

Example: 'Data store: Students file.'

DFD external entity Diagram

A person, organisation or element that provides data to the system or receives data from it (shown as a rectangle).

Example: 'External entity: Customer.'

DFD data flow (labelled arrow) Diagram

A labelled, curved arrow shows the flow of data between processes, data stores and external entities. Always label it with the data name.

Example: 'Arrow labelled Order details.'

Level 0 DFD (context diagram) Diagram

An overview of the whole system as one process; it does not show data stores or internal processes, only external entities and data flows.

Example: 'One circle: Library system with Member and Librarian.'

Level 1 DFD Diagram

Breaks the single process of the Level 0 diagram into its main processes and shows data stores and flows between them.

Example: 'Process 1 Borrow book, process 2 Return book, data store Loans.'

Check this one: The course specification gives the Level 0 diagram; Level 1 as a refinement is standard practice. Check how your teacher draws it.

Structure chart Diagram

Shows the separate subroutines that make up a system and their relationship to each other, top-down from the main routine.

Example: 'Main calls Get Data, Process Data, Display Results.'

Structure chart data couple (empty circle) Diagram

An empty circle indicates data movement between subroutines (usually passed as parameters).

Example: 'An arrow with an empty circle labelled mark.'

Structure chart flag (filled circle) Diagram

A filled circle indicates a flag or control variable passed between subroutines.

Example: 'Filled circle labelled Found.'

Structure chart decision (diamond) Diagram

A small diamond where lines meet shows optional execution of a subroutine called as the result of a selection.

Example: 'A report is not produced each time a book is returned.'

Structure chart repetition (curved arrow) Diagram

A curved arrow shows a subroutine or set of subroutines executed multiple times.

Example: 'Curved arrow over Process Item.'

Refinement Diagram

Providing successively more detail as needed; a lower-level subroutine is shown in its own structure chart with the same name.

Example: 'Expand Validate Input into its own chart.'

Class diagram Diagram

A visual representation of an object-oriented system: classes (name, attributes, methods) and the relationships between them.

Example: 'Person with Student and Parent inheriting from it.'

Class diagram inheritance and multiplicity Diagram

Inheritance is shown by an arrow from the subclass to the superclass. Multiplicity (1, 0..*, 1..*) shows how many objects can be related: a student studies 1 or more subjects; a subject has 0 or more students.

Example: 'Student ---- 1..* Subject.'

Entity relationship diagram (ERD) Diagram

Shows the tables (entities) in a database, their attributes and the relationships between them (one-to-one, one-to-many, many-to-many) using primary and foreign keys.

Example: 'Customer 1 to many Order.'

Check this one: Your school's drawing-questions page says the ERD is technically NOT in the syllabus (practice only); the course specification has no ERD symbols. Learn it as a low priority.

Storyboard Diagram

Shows the screens of an interface and the links (navigation) between them.

Example: 'Home page links to Menu and Contact pages.'

Decision tree (diagram) Diagram

Represents all possible combinations of decisions and their resulting actions. Each path leads to another decision or a final action.

Example: 'If temperature > 25 then fan on.'

Data dictionary (specification) Diagram

Describes every variable: name, data type, format for display, size in bytes, size for display, description, example and validation rules.

Example: 'DOB | Date | YYYY/MM/DD | 4 | 10 | birth date | 1953/10/05 | valid date before today.'

Gantt chart (specification) Diagram

Shows tasks on an estimated timeline with self-explanatory names, estimated time, dependent tasks, dates and milestones; can allocate resources and show percentage completion, and is updated with actual v estimated times.

Example: 'Design (1 wk) then Build (2 wk), dependent on Design.'

Process diary (log book) Diagram

Documents progress with regular entries: date, person, progress since last entry, tasks achieved, issues and how managed, upcoming approaches, reflective comments and resources used.

Example: 'Entry: 12 Mar, Sam, finished login, issue: bug fixed with debugger.'

Check this one: Not found word-for-word in the supplied syllabus, specifications, marking guidelines or notes; the definition is standard computing knowledge, so check it against your class notes.

Wiring diagram Diagram

Uses standard symbols (resistor, capacitor, diode, LED, switch, motor, speaker, voltage source) to show how mechatronic components are connected; label any extra components.

Example: 'A battery, switch and LED in series.'

Flowchart Diagram

Represents an algorithm with standard symbols connected by lines with arrowheads, read top to bottom and left to right, using only the standard control structures. Label arrows leaving a decision (Yes or No).

Example: 'Diamond: age >= 18? Yes: Display Adult.'

Mainline and subroutines (algorithms) Diagram

Start complex algorithms with a clear, uncluttered mainline that calls subroutines; the details of each subroutine are in separate algorithms.

Example: 'BEGIN Main: GetData, Process, Display END.'